Plant care guide
Spider Mites on Hydrangeas: Spot the Stippling, Then Act
Updated
Why does my Hydrangea have spider mites?
Fine pale freckling on hydrangea leaves, sometimes with silk webbing underneath, is the mark of two-spotted spider mites. They build up fast in hot, dry weather and on plants short of water, in the garden or on a potted hydrangea indoors.
What to do first
Confirm with a hand lens or by tapping a leaf over white paper. Hose or rinse the leaf undersides hard, water the plant deeply in dry spells, and use insecticidal soap or horticultural oil if mites persist. Avoid broad-spectrum insecticides, which kill mite predators.
Spider mites are easy to miss on a hydrangea. The leaves just look dull or faintly speckled at first. The UConn Home & Garden Education Center’s hydrangea factsheet lists the two-spotted spider mite as a hydrangea pest. It says the leaves take on a stippled or freckled look, sometimes with webbing.
Each tiny pale dot is a feeding wound. Catch them early and water alone often brings them under control.
Confirm it’s spider mites
The damage. Penn State Extension’s twospotted spider mite page explains that mites drain individual leaf cells. As chlorophyll is lost, the leaf turns light brown, white or yellow. UC IPM’s spider mite pest note says leaves may later bronze, turn yellow or reddish and drop.
The mites. UC IPM says adults are under 1.3 mm (1/20 in) long, oval, with eight legs. They live mainly on leaf undersides, often with silk webbing. You’ll need a hand lens.
The paper test. UC IPM suggests shaking a leaf over white paper. Mites that fall off move around quickly.
| What you see | More likely |
|---|---|
| Fine pale stippling, dusty webbing underneath | Spider mites |
| Round tan spots with purple or reddish-brown rims | Cercospora leaf spot |
| Sticky honeydew, black sooty mould on upper leaves, insects under the leaves | Cottony camellia scale |
| Whole plant limp on hot afternoons, perking up by evening | Heat stress |
University of Maryland Extension’s hydrangea problems page describes cottony camellia scale feeding on leaf undersides and leaving honeydew and sooty mould.
Why hydrangeas get them
UConn says spider mites are most active in hot, dry weather. Penn State says they reproduce faster, with more generations a year, when it is consistently hot. UC IPM adds that they favour dusty conditions and water-stressed plants.
That fits hydrangeas. Maryland notes they are among the first plants to wilt during dry periods and in full sun. A thirsty hydrangea in a hot, sunny spot is a good mite host. Indoors, Washington State University’s spider mite fact sheet says the warm, dry air of most homes suits them too.
What to do
- Water deeply. UConn advises keeping plants adequately watered during dry periods, so they withstand the injury. UC IPM agrees that preventing water stress helps.
- Spray the undersides with water. Penn State says a strong blast from a hose can dislodge mites from foliage tough enough to take it. UC IPM says forceful water sprays often reduce mite numbers.
- Rinse potted plants indoors. WSU suggests rinsing houseplants thoroughly in a shower or sink with lukewarm water, and isolating them.
- Use soap or oil if they persist. UC IPM and Penn State both favour insecticidal soap or horticultural oil. Cover the leaf undersides thoroughly. UC IPM warns against using either on water-stressed plants or above 32 °C (90 °F). Water first and spray in the cool of the day.
- Protect the predators. UConn says naturally occurring predators usually control outdoor mites. Penn State names lady beetles, predatory mites, lacewings and pirate bugs. Both warn that broad-spectrum insecticides make mite problems worse by killing them.
In a greenhouse or conservatory, the RHS red spider mite page suggests the predatory mite Phytoseiulus persimilis as a biological control. It says regular spraying with water and high humidity reduce mite numbers, though they won’t control them alone.
After treatment
Stippled leaves won’t turn green again. Judge success by new leaves and by fewer mites in the paper test.
Check again a week later. Penn State notes eggs take 7 to 20 days to hatch, depending on temperature, so a single treatment can miss mites that hatch later.
Prevent it
- Water deeply in dry spells.
- Give bigleaf hydrangeas some afternoon shade. Our hydrangea heat wilting guide explains how.
- Check new potted hydrangeas before they join other plants. WSU suggests quarantining new houseplants for about a month.
- Scout leaf undersides from early summer. Penn State suggests late May or early June.
Round spots with purple rims rather than stippling point to Cercospora leaf spot, which needs clean-up and dry leaves instead. For mites on houseplants generally, see spider mites on houseplants. The hydrangea hub collects our other hydrangea pages.
Related guides
Other hydrangea problems we cover: brown spots.
References
- UConn Home & Garden Education Center: Hydrangea Diseases and Pests
- UC IPM: Pest Notes: Spider Mites (Publication 7405)
- Penn State Extension: Twospotted Spider Mites
- Washington State University Extension, PestSense: Spider mites
- RHS: Glasshouse red spider mite
- University of Maryland Extension: Hydrangea, identify and manage problems
How this guide was put together: UConn Home & Garden Education Center, UC IPM, Penn State Extension, Washington State University Extension, RHS and University of Maryland Extension guidance.